Temperature sensor

ABSTRACT

A temperature sensor comprises (a) a first voltage generating circuit that generates and outputs a first voltage having a positive or negative temperature coefficient in proportion to the absolute temperature; (b) a second voltage generating circuit that generates a second voltage having an opposite sign of temperature coefficient compared to the first voltage and outputs a reference voltage that does not have a temperature coefficient based on the second voltage; and (c) a comparator that compares the first voltage output from the first voltage generating circuit with the reference voltage output from the second voltage generating circuit.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention generally relates to a temperature sensor,and more particularly, to a temperature sensor for detecting theoperating temperature of, for example, an LIS or other semiconductordevices, which is capable of stable operation in a high temperaturerange, while realizing at least one of a highly sensitive operating modeand a low-voltage operating mode.

[0003] 2. Description of the Related Art

[0004] If an abnormally large quantity of electric current flows througha semiconductor integrated circuit, or if the temperature of thesemiconductor integrated circuit rises too high due to the environmentalchange, the semiconductor integrated circuit will be destroyed. Toprevent the destruction, the operation of the semiconductor integratedcircuit has to be stopped before the detected temperature reaches thecritical temperature. To this end, a temperature sensor or a temperatureprotection circuit is generally incorporated in the semiconductorintegrated circuit to prevent the circuit from being damaged. Such atemperature sensor includes a PTAT voltage generator that generates avoltage proportional to the absolute temperature (which is referred toas a “PTAT voltage”), and a reference voltage generator for generating areference voltage. The outputs from the PTAT voltage generator and thereference voltage generator are compared at a comparator, which is alsoincluded in the temperature sensor.

[0005] When the PTAT voltage exceeds the reference voltage (which is thetarget temperature at which the operation of the semiconductorintegrated circuit has to be stopped), a chip enable (CE) signal forstopping the semiconductor integrated circuit is activated.

[0006] Both the PTAT voltage and the reference voltage have to be veryprecise, because if the precision of these voltages is degraded, the CEsignal may be activated in spite of the fact that the semiconductorintegrated circuit operates at an acceptable operating temperature, orthe CE signal may not be activated even if the temperature exceeds theacceptable operative temperature. In the latter case, the semiconductorintegrated circuit will be destroyed. Therefore, it is important for thetemperature protection circuit to output the PTAT voltage and thereference voltage at high precision.

[0007]FIG. 1 illustrates a semiconductor temperature sensor disclosed inJPA H9-243466, which includes two MOS transistors N1 and N2 havingdifferent W/L ratios of the channel width W to the channel length L. Ifthe same electric current Id is supplied from the constant voltagesource 11, the gate-source voltages Vgs1 and Vgs2 generated attransistors N1 and N2 differ from each other. The potential differencebetween the two gate-source voltages (Vgs1-Vgs2) is in proportion to theoperating temperatures of the transistors N1 and N2, and therefore, thisvoltage difference can be used as a PTAP signal. By adjusting the W/Lratios of the two MOS transistors N1 and N2, a signal having a positiveor negative temperature coefficient can be obtained.

[0008]FIG. 2 illustrates another example of the temperature sensor, inwhich an NPN transistor or a PNP transistor is inserted bydiode-connection. When a constant current is supplied, voltage Vt havinga negative temperature coefficient appears between both ends of thediode. If the Vt exceeds the reference voltage Vref, a prescribed signalTout is output from the comparator.

[0009] However, there is a problem in the semiconductor temperaturesensor shown in FIG. 1 that outputs the potential difference between thegate-source voltages Vgs of two MOS transistors. The problem is that thetemperature range for accurately extracting the PTAP voltage islimited-to the range from −50° C. to 100° C. The accuracy of the PTAPvoltage cannot be guaranteed at a higher temperature above 100° C., atwhich the semiconductor integrated circuit is very likely to bedestroyed.

[0010] The circuit shown in FIG. 2 using a diode connection is alsodisadvantageous because the PTAP voltage is adversely affected byprocess variation, and is incapable of outputting a precise PTATvoltage. In addition, the slope of the PTAT voltage in proportion to theabsolute temperature (i.e., the temperature slope) cannot be adjustedfreely because the temperature slope is fixed by the process. Thestructure shown in FIG. 2 is lacking in flexibility for designingdifferent types of circuits, such as a highly precise temperaturesensing circuit with a large temperature slope, or a low-voltageoperating circuit with a small temperature slope.

[0011] Another problem in the prior art techniques is difficulty inproducing a constant and stable reference voltage, with which thedetected PTAT voltage is compared, independently of the temperature.

SUMMARY OF THE INVENTION

[0012] Therefore, it is an object of the present invention to provide atemperature sensor that is accurate even at a high operating temperatureand has a flexibly selected temperature slope to improve the sensitivityor to allow a low-voltage operation.

[0013] By making the temperature slope adjustable, the temperaturesensor can be designed for a desired operation mode, such as a highlysensitive operating mode, or a low-voltage operating mode.

[0014] It is another object of the invention to provide a highlysensitive and low-voltage operating temperature sensor. This is achievedby inserting a subtraction circuit in the temperature sensor. In thiscase, the output PTAT voltage can be reduced, while maintaining highsensitivity.

[0015] To achieve the object, the present invention makes use of theprinciple of difference in gate work function, the details of which aredisclosed in U.S. Pat. No. 6,437,550.

[0016] In one aspect of the invention, a temperature sensor comprises(a) a first voltage generating circuit that generates and outputs afirst voltage having a positive or negative temperature coefficient inproportion to the absolute temperature; (b) a second voltage generatingcircuit that generates a second voltage (Vpn) having an opposite sign oftemperature coefficient to the first voltage, and outputs a referencevoltage that does not have a temperature coefficient based on the secondvoltage; and (c) a comparator that compares the first voltage outputfrom the first voltage generating circuit with the reference voltageoutput from the second voltage generating circuit.

[0017] The first voltage generating circuit includes a first transistorhaving a highly-doped n-type gate, a second transistor having alightly-doped n-type gate, and a source follower that gives a gatepotential to the second transistor.

[0018] The source follower is comprised of a third transistor and two ormore resistors whose resistance values are adjustable, and the firstvoltage is output from the source follower to the comparison circuit.

[0019] With this structure, the temperature sensor makes use of thedifference in gate work function to produce a PTAT voltage, andtherefore, it is capable of stable operation even at a high temperature.

[0020] In addition, the temperature coefficient (or slope) of the PTATvoltage (that is, the first voltage) can be easily adjusted by simplyadjusting the resistance values of the source follower.

[0021] The second voltage generating circuit includes a first transistorhaving a highly-doped n-type gate, a second transistor having ahighly-doped p-type gate, and a source follower giving a gate potentialto the second transistor.

[0022] The source follower is comprised of a third transistor and two ormore resistors whose resistance values are adjustable, and the referencevoltage is output from the source follower to the comparison circuit.

[0023] With this structure, the second voltage is generated making useof the difference in gate work function, and a stable reference voltagecan be output.

[0024] In another aspect of the invention, a temperature sensorcomprises (a) a first voltage generating circuit that generates a firstvoltage having a positive or negative temperature coefficient; (b) asecond voltage generating circuit that generates a first referencevoltage and a second reference voltage that do not have a temperaturecoefficient; (c) a subtraction circuit that subtracts the firstreference voltage supplied from the second voltage generating circuitfrom the first voltage supplied from the first voltage generatingcircuit and outputs a subtraction result; and (d) a comparison circuitthat compares the subtraction result output from the subtraction circuitwith the second reference voltage supplied form the second voltagegenerating circuit, and outputs a comparison result.

[0025] With this structure, the voltage level is reduced at thesubtraction circuit even if the temperature coefficient (or slope) isincreased for higher sensitivity. Accordingly, high-sensitivityoperations and low-voltage operations are simultaneously realized.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Other objects, features, and advantages of the present inventionwill become more apparent from the following detailed description whenread in conjunction with the accompanying drawings, in which:

[0027]FIG. 1 illustrates a prior art circuit for generating a PTAPvoltage;

[0028]FIG. 2 illustrates a prior art circuit for obtaining a temperaturedetection signal;

[0029]FIG. 3 is a block diagram of the temperature sensor according tothe first embodiment of the invention;

[0030]FIG. 4 is a circuit diagram of the temperature sensor shown inFIG. 3;

[0031]FIG. 5 is a graph showing Tvptat voltage and Tvref voltage as afunction of temperature, which are generated by the circuit shown inFIG. 4;

[0032]FIG. 6 is a graph showing the Tvptat voltage and Vptat voltage asa function of temperature, which are output from the first voltagegenerating circuit shown in FIG. 4;

[0033]FIG. 7 illustrates a series of resistance, which can be trimmed toadjust the Tvptat and Tvref output from the first voltage generatingcircuit;

[0034]FIG. 8 is a circuit diagram showing a modification of thetemperature sensor according to the first embodiment;

[0035]FIG. 9 is a circuit diagram showing another modification of thetemperature sensor according to the first embodiment;

[0036]FIG. 10 is a graph used to explain the operation of thetemperature sensor shown in FIG. 9;

[0037]FIG. 11 is a graph used to explain the relation between thesensitivity and the operation voltage in the temperature sensor of thefirst embodiment;

[0038]FIG. 12 is a block diagram of the temperature sensor according tothe second embodiment of the invention;

[0039]FIG. 13 is a circuit diagram of the temperature sensor shown inFIG. 12;

[0040]FIG. 14A through FIG. 14D are graphs showing the temperaturecharacteristics of various signals generated in the circuit shown inFIG. 13;

[0041]FIG. 15 is a circuit diagram of a modification of the temperaturecircuit of FIG. 13;

[0042]FIG. 16A through FIG. 16D are graphs showing the temperaturecharacteristics of various signals generated in the circuit shown inFIG. 15;

[0043]FIG. 17 is a block diagram of the temperature sensor according tothe third embodiment of the invention;

[0044]FIG. 18 is a circuit diagram of the temperature sensor shown inFIG. 17;

[0045]FIG. 19A through 19D are graphs showing the temperaturecharacteristics of various signals generated in the circuit shown inFIG. 18;

[0046]FIG. 20 is a circuit diagram of a modification of the temperaturesensor shown in FIG. 18;

[0047]FIG. 21 is a graph showing the operation characteristics of thecircuits of the first through third embodiments;

[0048]FIG. 22 is a block diagram of the temperature sensor according tothe fourth embodiment of the invention;

[0049]FIG. 23 is a circuit diagram of the temperature sensor shown inFIG. 22;

[0050]FIG. 24A through FIG. 24E are graphs showing the temperaturecharacteristics of various signals generated in the circuit shown inFIG. 23;

[0051]FIG. 25 is a, block diagram of the temperature sensor according tothe fifth embodiment of the invention;

[0052]FIG. 26 is a circuit diagram of the temperature sensor shown inFIG. 25;

[0053]FIG. 27A through FIG. 27E are graphs showing the temperaturecharacteristics of various signals generated in the circuit shown inFIG. 26;

[0054]FIG. 28 is a graph showing the operation characteristics of thetemperature sensor of the fourth embodiment, in comparison with that ofthe first embodiment; and

[0055]FIG. 29 is a graph showing the operation characteristics of thetemperature sensor of the fifth embodiment, in comparison with that ofthe first embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0056] The details of the present invention will now be described withreference to the attached drawings.

[0057] <First Embodiment>

[0058]FIG. 3 is a block diagram of the temperature sensor according tothe first embodiment of the invention. The temperature sensor comprisesa first voltage generating circuit A, a second voltage generatingcircuit B, and a comparison circuit C. The first voltage source Aoutputs a PTAT voltage (referred to as “Tvptat” in the firstembodiment,), which has a positive temperature coefficient in proportionto the absolute temperature, as well as a voltage Vptat′, which also hasa positive temperature coefficient and is obtained from Tvptat through avoltage-divider. Tvptat is supplied to the comparison circuit for thecomparison with the reference voltage. On the other hand, Vptat′ issupplied to the second voltage generating circuit for obtaining areference voltage.

[0059] The second voltage generating circuit B generates a voltagehaving a negative temperature coefficient, and adds this voltage toVptat′ supplied from the first voltage generating circuit A to output afirst reference voltage Vref. The second voltage generating circuit Balso outputs a second reference voltage Tvref, which is obtained formVref through voltage conversion at a predetermined ratio. Both the firstand second reference voltages Vref and Tvref are independent of thetemperature coefficient.

[0060] The comparison circuit C compares Tvptat output from the firstvoltage generating circuit A with the second reference voltage Tvrefoutput from the second voltage generating circuit B, and outputs acomparison result Tout.

[0061] The first voltage generating circuit A makes use of the principleof difference in gate work function, and therefore, it is capable ofproducing Tvptat and Vptat′ at high precision almost up to the marginaloperating temperature of the semiconductor device. The second voltagegenerating circuit B also makes use of the principle of difference ingate work function when producing the voltage having a negativetemperature coefficient. Consequently, Vref and Tvref can be generatedin a stable manner almost up to the marginal operative temperature ofthe semiconductor device.

[0062]FIG. 4 is a circuit diagram of the temperature sensor shown inFIG. 3. In the example shown in FIG. 4, the circuit of the temperaturesensor is formed on an n-type substrate.

[0063] The first voltage generating circuit comprises n-channel fieldeffect transistors (hereinafter, simply referred to as “n-typetransistor”) M1, M2, and M3, and resistors R1, R2 and R5. Transistors M1and M2 are formed in the p-type well of the n-type substrate, and havethe same impurity concentration at the channel regions and thesource/drain regions. The electric potential of the substrate of eachtransistor is equal to the source potential. The ratios (W/L) of thechannel width W to the channel length L of the-transistors M1 and M2 areset equal to each other.

[0064] Transistor M1 has a highly-doped n-type gate, and transistor M2has a lightly-doped n-type gate. Transistors M1 and M2 are connected inseries. The gate of transistor M1 is coupled to its source. Thus, thetransistor M1 is used as a constant-current source. Transistor M3 andresistors R1, R2, and R5, which are connected in series, comprise asource follower. While Tvptat is output from the junction point betweenthe source of transistor M3 and resistor R1, Vptat′ is output from thejunction point between resistors R1 and R2. The electric potentialbetween resistors R2 and R5, which is represented as Vptat, is connectedto the gate of transistor M2. The Vptat represents a physical quantityoriginally generated in proportion to the absolute temperature. Tvptatand Vptat′ are obtained from Vptat through voltage conversion atpredetermined ratios.

[0065] The second voltage generating circuit comprises n-typetransistors M4 and M5, p-channel field effect transistors (hereinafter,simply referred to as “p-type transistors”) M6, M7, M8, and resistors R3and R4. Transistors M4 and M5 are formed in the p-type well of then-type substrate, and have the same impurity concentration of thesubstrate and the channel dope regions. The electric potential of thesubstrate of each transistor is equal to the source potential. Theratios (W/L) of the channel width W to the channel length L of thetransistors M4 and M5 are set equal to each other.

[0066] Transistor M4 has a highly-doped n-type gate, and transistor M5has a highly-doped p-type gate. The pair of transistors M4 and M5, whichare substantially the same except for the gate polarities, function asinput transistors of a differential amplifier. Transistors M6 and M7form a current-mirror circuit, and therefore, the same quantity ofelectric current flows through the drains of transistors M4 and M5. Thedifferential amplifier (M4 and M5) and transistor M8 form a feedbackloop. The voltage Vref at the gate of transistor M5 is divided betweenresistors R3 and R4, and supplied as Tvref to the comparison circuit.

[0067] The comparison circuit comprises n-type transistors M9, M10, andM14, and p-type transistors M11, M12, and M13. Transistors M11 and M12form a current-mirror circuit. Transistors M9 and M10 are inputtransistors of a differential amplifier. Tvref is applied to the gate oftransistor M9 from the second voltage generating circuit, and Tvptat isapplied to the gate of transistor M10 from the first voltage generatingcircuit. This differential amplifier (M9 and M10) is used as acomparator. The output of the differential amplifier is supplied to theoutput buffer consisting of p-type transistor M13 and n-type transistorM14. The output of the output buffer is Tout, which is the output of thecomparison circuit.

[0068] In FIG. 4, the n-type transistor M2 with a lightly-doped n-typegate is marked with a triangle, while the n-type transistor M5 with ahighly doped p-type gate is circled, because these transistors are notordinary. This arrangement applies to the subsequent modifications andembodiments.

[0069] In operation, in the first voltage generating circuit, the samedrain current flows through the pair of transistors M1 and M2 that areof the same conductivity type and with different impurityconcentrations. Since the potential difference between the source andthe gate (i.e., the source-gate voltage) of transistor M1 is 0V, thepotential difference between the source-gate voltages of transistors M1and M2 is equal to the source-gate voltage of transistor M2, which thenbecomes a voltage in proportion to the absolute temperature. Thisvoltage is referred to as Vptat.

[0070] Accordingly, Vptat′ supplied to transistor M4 of the secondvoltage generating circuit becomes

Vptat′=Vptat*(R 2+R 5)/R 5.   (1)

[0071] On the other hand, Tvptat supplied to transistor M10 of thecomparison circuit becomes

Tvptat=Vptat*(R 1+R 2+R 5)/R 5.   (2)

[0072] Since Vptat has a positive temperature coefficient, Vptat′ andTvptat also have positive temperature coefficients.

[0073] In the second voltage generating circuit, a pair of transistorsM4 and M5 having opposite gate polarities function as input transistorsof the differential amplifier, while p-type transistors M6 and M7 form acurrent-mirror circuit. Accordingly, the same quantity of electriccurrent flows through the drains of transistors M4 and M5. Thedifferential amplifier (M4 and M5) and transistor M8 form a feedbackloop, and therefore, input offset Vpn is generated between the gate oftransistor M4 and the gate of transistor M5. The offset voltage Vpn hasa negative temperature coefficient.

[0074] Consequently, when Vptat′ is applied to the gate of transistor M4from the first voltage generating circuit, a certain voltage Vx that isproduced by adding the offset voltage Vpn to Vptat′ appears at the gateof transistor M5.

[0075] Because Vx is the sum of Vptat′ having a positive temperaturecoefficient and Vpn having a negative temperature coefficient, Vx doesnot have a temperature characteristic, and it becomes a constantreference voltage Vref. Voltage Tvref supplied to the transistor M9 ofthe comparison circuit can be obtained from Vref. Tvref is expressed as

Tvref=Vref*R 4/(R 3+R 4).   (3)

[0076] The product Tvref does not have a temperature coefficient.

[0077] In the comparison circuit, p-type transistors M11 and M12 form acurrent-mirror circuit, and a pair of n-type transistors M9 and M10 arethe input transistors of the differential amplifier. Tvref is input tothe gate of the transistor M9 from the second voltage generatingcircuit, and Tvptat is input to the gate of the transistor M10 from thefirst voltage generating circuit. Since Tvref does not have atemperature coefficient, it is constant even if the temperature changes.On the other hand, Tvpat has a positive temperature coefficient, and thevoltage Tvpat increases in proportion to the temperature rise, asillustrated in FIG. 5.

[0078] Either Tvref or Tvpat is adjusted so that the characteristiclines of these two voltages cross each other at a desired temperature Tselected to protect the semiconductor integrated circuit, as illustratedin FIG. 5. If the detected temperature is below the selected temperatureT, Tvptat is smaller than Tvref (Tvptat<Tvref), and the output from thecomparator (M9, M10) becomes High. The output Tout of the temperaturesensor becomes Low.

[0079] If the temperature rises and the detected temperature exceeds theselected temperature T, then Tvptat becomes greater than Tvref(Tvptat>Tvref). The output of the comparator (M9, M10) becomes Low, andthe final output of the temperature sensor becomes High. The outputsignal Tout is used as a chip enable signal to protect the semiconductorintegrated circuit.

[0080] Tvref can be set to a desired level by adjusting the ratio of R3to R4, as expressed in equation (3). In order to set Tvptat to a desiredlevel, the ratio of (R1+R2+R5) to R5 is adjusted, as expressed inequation (2).

[0081] Since Tvptat equals Vptat*(R1+R2+R5)/R5, the. temperature slope,that is, the voltage change Δ Tvptat with respect to a temperaturechange of one degree also equals (R1+R2+R5)/R5 times ΔVptat. If theslope of Tvptat (ΔTvptat) is set large, variation in Tvref due tofluctuation of the ratio R3 to R4 can be absorbed, as long as thevariation is within ΔTvptat. Accordingly, a highly sensitive temperaturesensor can be realized by setting the slope of Tvptat large.

[0082] On the other hand, if the slope of Tvptat (ΔTvptat) is set small,the output voltage Tvptat will not rise too much even if the detectedtemperature reaches the target temperature T. Accordingly, theoperational voltage of the temperature sensor can be maintained low. Thelevel of Tvptat can be regulated easily by adjusting resistance R1, R2,and R3. Tvref can also be regulated easily by adjusting resistance R3and R4. The ratio of the resistances may be fixed to a preferred valueduring the fabrication of the circuit. Alternatively, the resistancevalues of each resistor may be adjusted by laser-trimming the resistorsat the cross-marked positions shown in FIG. 7, after the circuit isfabricated.

[0083] The reference voltage Vref generated by the second voltagegenerating circuit can be used as an external reference voltage suppliedto the semiconductor integrated circuit. Since the above-describedvoltages are generated making use of the difference in work function ofthe gate, these voltages can be output accurately even at or near themarginal operating temperature of the semiconductor device, withoutbeing adversely affected by the actual operation temperature.

[0084]FIG. 8 illustrates a modification of the temperature sensor of thefirst embodiment. In the modification, the temperature sensor is formedon a p-type substrate. The temperatures sensor comprises a first voltagegenerating circuit, a second voltage generating circuit, and acomparison circuit, as in the circuit shown in FIG. 4.

[0085] The first voltage generating circuit comprises p-type transistorsM1, M2, and M3, and resistors R6, R7 and R8. Transistors M1 and M2 areformed in the n-type well of the p-type substrate, and have the sameimpurity concentration at the channel regions and the source/drainregions. The electric potential of the substrate of each transistor isequal to the source potential. The ratios (W/L) of the channel width Wto the channel length L of the transistors M1 and M2 are set equal.Transistor M2 has a lightly-doped n-type gate, and it is used as aconstant current source with the gate connected to its source.

[0086] Transistor M1 has a highly doped n-type gate, and its gatevoltage is defined by the source follower circuit comprised oftransistor M3 and resistor R6. The electric potential between the sourceand gate (i.e., the source-gate voltage) of transistor M1 is Vptat,which is originally produced in proportion to the absolute temperature.Voltage Vptat′ is extracted from the drain of transistor M3. Anothervoltage Tvptat is extracted from the junction point between resistor R7and R8.

[0087] The second voltage generating circuit comprises n-typetransistors M4 and M5, p-type transistors M6, M7, and M8, and resistorsR9 and R10. Transistors M4 and M5 are formed in the p-type substrate,and have the same impurity concentration of the substrate and thechannel dope regions. The electric potential of the substrate of eachtransistor is equal to the ground potential. The ratios (W/L) of thechannel width W to the channel length L of the transistors M4 and M5 areset equal to each other.

[0088] Transistor M4 has a highly-doped n-type gate, and transistor M5and a highly-doped p-type gate. The pair of transistors M4 and M5function as input transistors of a differential amplifier. The p-typetransistors M6 and M7 form a current-mirror circuit. The differentialamplifier (M4 and M5) and p-type transistor M8 form a feedback loop.Reference voltage Vref is output from the differential amplifier (M4,M5). By dividing Vref between resistors R9 and R10, another referencevoltage Tvref is produced and supplied to the comparison circuit.

[0089] The comparison circuit comprises n-type transistors M9, M10, andM14, and p-type transistors M11, M12, and M13. Transistors M11 and M12form a current-mirror circuit. Transistors M9 and M10 function as inputtransistors of a differential amplifier. Tvref is applied to the gate oftransistor M9 from the second voltage generating circuit, and Vptat isapplied to the gate of transistor M10 from the first voltage generatingcircuit. The output of the differential amplifier (M9 and M10) issupplied to the output buffer consisting of p-type transistor M13 andn-type transistor M14. The output of the output buffer is Tout, which isthe output of the comparison circuit.

[0090] In operation, in the first voltage generating circuit, the samequantity of electric current flows through the pair of transistors M1and M2, and the source-gate voltage of transistor M1 becomes Vptat, asin the previous example. Since electric current flowing through resistorR6 also flows through resistors R7 and R8, Vptat′ is expressed as

Vptat′=Vptat*(R 7+R 8)/R 6.   (4)

[0091] Furthermore, Tvptat extracted from the junction point between R7and R8 is expressed as

Tvptat=Vptat*R 8/(R 7+R 8).   (5)

[0092] Because Vptat has a positive temperature coefficient, Vptat′ andTvptat also have positive temperature coefficients.

[0093] In the second voltage generating circuit, a pair of transistorsM4 and M5 having opposite gate polarities function as input transistorsof the differential amplifier, and p-type transistors M6 and M7 form acurrent-mirror circuit. Accordingly, the same-quantity of electriccurrent flows through the drains of transistors M4 and M5. Thedifferential amplifier (M4 and M5) and transistor M8 form a feedbackloop, and accordingly, an input offset Vpn occurs between the gate oftransistor M4 and the gate of transistor M5. The offset Vpn has anegative temperature coefficient.

[0094] Consequently, when Vptat′ is applied to the gate of thetransistor M4 from the first voltage generating circuit, the referencevoltage Vref, which is the sum of Vptat′ and Vpn, appears at the gate ofthe transistor M5.

[0095] Because Vref is obtained by adding Vpn having a negativetemperature coefficient to Vptat′ having a positive temperaturecoefficient, Vref does not have a temperature characteristic. This Vrefbecomes a constant reference voltage. Another reference voltage Tvref isproduced from Vref, which is to be supplied to the transistor M9 of thecomparison circuit. Tvref is expressed as

Tvref=Vref*R 10/(R 9+R 10).   (6)

[0096] The product Tvref does not have a temperature coefficient.

[0097] In the comparison circuit, p-type transistors M11 and M12 form acurrent-mirror circuit, and a pair of n-type transistors M9 and M10function as input transistors. Tvref is input to the gate of thetransistor M9 from the second voltage generating circuit, and Tvptat isinput to the gate of the transistor M10 from the first voltagegenerating circuit. Since Tvref does not have a temperature coefficient,it is constant even if the temperature changes. On the other hand, Tvpathas a positive temperature coefficient, and the voltage Tvpat increasesin proportion to the temperature rise.

[0098] If the detected temperature is below the selected temperature T,Tvptat is smaller than Tvref (Tvptat<Tvref), and the output from thecomparator (M9, M10) becomes High. Consequently, the output Tout of thecomparison circuit becomes Low. If the temperature rises and thedetected temperature exceeds the selected temperature T, then Tvptatbecomes greater than Tvref (Tvptat>Tvref). The output of the comparator(M9, M10) becomes Low, and the final output of the comparison circuitbecomes High. The output signal Tout is used as a chip enable signal toprotect the semiconductor integrated circuit.

[0099] Tvref can be set to a desired level by adjusting the ratio of R9to R10. To set Tvptat to a desired level, the ratio (R7+R8)/R6 isadjusted.

[0100]FIG. 9 illustrates a second modification of the first embodiment.In the second modification, the temperature sensor has two comparisoncircuits to sense two different temperatures. The second voltagegenerating circuit generates two types of reference voltage Tvref1 and,Tvref2, which are supplied to the first and second comparison circuits,respectively. The first voltage generating circuit generates Vptat inproportion to the absolute temperature, and creates Tvptat and Vptat′based on Vptat. The Tvptat is supplied to the first and secondcomparison circuits for the comparison with the first and secondreference voltages Tvref1 and Tvref2, respectively.

[0101] With this temperature sensor, the first temperature T1 isdetected using the first reference Tvref1, and the second temperature isdetected using the second reference Tvref2, as illustrated in FIG. 10.This modification is advantageous because the operation of thesemiconductor integrated circuit can be controlled more flexibly andprecisely by slowing down the operation rate of the semiconductorintegrated circuit at the first temperature T1, and by stopping theoperation of the semiconductor integrated circuit at the secondtemperature T2.

[0102]FIG. 11 illustrates the temperature slope of the Tvptat outputfrom the first voltage-generating circuit, as a function of-temperature.As has been described above, the slope of Tvptat is adjustable to adesired level through a voltage-divider. When the slope (that is, thetemperature coefficient) is set to Tvptat 2, which is greater thanTvptat 1, the sensitivity is improved. However, the operating voltagealso rises, and according, low-voltage operation becomes difficult at ornear the target temperature. On the other hand, by setting the slopesmaller as in the case of Tvptat 1, the temperature sensor can operateat a low voltage.

[0103] In this manner, with the temperature sensor of the firstembodiment, either sensitive temperature detection or a low-voltageoperation can be realized by adjusting the slope of Tvptat using asimple voltage-divider.

[0104] In addition, a stable and constant reference voltage can beproduced by generating an offset voltage having a slope with a polarityopposite to the PTAT voltage.

[0105] As a whole, the temperature sensor can operate precisely even ator near the marginal operating temperature of the semiconductor device.

[0106] In the first embodiment, the first voltage generating circuitgenerates a voltage having a positive temperature coefficient, while thesecond voltage generating circuit generates a voltage having a negativetemperature coefficient. However, a voltage with a negative coefficientmay be generated from the first voltage generating circuit, while avoltage with a positive temperature coefficient is generated by thesecond voltage generating circuit.

[0107] Any type of temperature detection circuit can be used as thefirst voltage generating circuit of the first embodiment, as long as itcan generate a voltage in proportion to the absolute temperature. Such avoltage can be used in place of Tvptat with a positive temperaturecoefficient in the first embodiment.

[0108] Although, in the first embodiment, Vptat′ is supplied from thefirst voltage generating circuit to the second voltage generatingcircuit, Vptat′ may be generated in the second voltage generatingcircuit. In this case, the second voltage generating circuit producesthe reference voltage by adding Vpn to Vptat′, both of which aregenerated in the second voltage generating circuit so as to haveopposite sign of temperature coefficients.

[0109] <Second Embodiment>

[0110]FIG. 12 is a block diagram of the temperature sensor according tothe second embodiment. The temperature sensor comprises a first voltagegenerating circuit, a second voltage generating circuit, a subtractioncircuit, and a comparison circuit. In the second embodiment, the outputof the subtraction circuit is compared with the reference voltage. Thisarrangement is capable of reducing the operating voltage, whilemaintaining high sensitivity.

[0111] The first voltage generating circuit generates a voltage Svptatin proportion to the absolute temperature. Svptat has either a positiveor negative temperature coefficient. This Svptat is supplied to thesubtraction circuit. The second voltage generating circuit generates afirst reference voltage Vref, a second reference voltage Tvref, and athird reference voltage Svref, none of which has a temperaturecoefficient. While the second reference voltage Tvref is supplied to thecomparison circuit, the third reference voltage Svref is supplied to thesubtraction circuit. The subtraction circuit amplifies the differencebetween Svptat and Svref, and outputs Tvptat to the comparison circuit.The comparison circuit compares the Tvptat with Tvref to output acomparison result Tout.

[0112] In the second embodiment, the second voltage generating circuitmakes use of the principle of difference in gate work function, whilethe first voltage generating circuit may or may not utilize thedifference of gate work function.

[0113]FIG. 13 is a circuit diagram of the temperature circuit shown inFIG. 12. This circuit is formed in an n-type substrate. The firstvoltage generating circuit is comprised of an NPN transistor Tr1. Thebase of Tr1 is coupled to its collector, and the emitter is connected tothe ground voltage GND, thereby outputting Svptat from the collector.The NPN transistor Tr1 can be fabricated by forming a base connected tothe p-type well formed in the n-type substrate, and forming an emitterand a collector connected to the n-type diffusion layers formed in thep-type well.

[0114] The second voltage generating circuit is comprised of a firstreference voltage generating circuit and a second reference voltagegenerating circuit. The first reference voltage generating circuitproduces voltage Vptat′. Vptat′ is supplied to the second referencevoltage generating circuit to create the reference voltage.

[0115] The first reference voltage generating circuit includes n-typetransistors M1, M2, and M3, and resistors R2 and R3. The n-typetransistors M1 and M2 are formed in the p-well of the n-type substrate,and have the same impurity concentration at the substrate and channeldope regions. The substrate potential of each transistor is equal to itssource voltage. The n-type transistor M1 has a highly-doped n-type gate,and n-type transistor M2 has a lightly doped n-type gate. The ratios(W/L) of the channel width W to the channel length L of these twotransistors are equal to each other.

[0116] The n-type transistors M1 and M2, which are substantially thesame except for the impurity concentrations of the gates, are connectedin series. The gate of n-type transistor M1 is coupled to its source.The transistor M1 is used as a constant-current source.

[0117] N-type transistor M2 has a gate voltage defined by the sourcefollower formed by n-type transistor M3 and resistors R2 and R3. Vptatis extracted from the junction point between resistors R2, R3, and thegate of n-type transistor M2. Vptat′ is extracted from the junctionpoint between the source of n-type transistor M3 and resistor R2.

[0118] The second reference voltage generating circuit comprises p-typetransistors M4, M5, and M8, n-type transistors M6 and M7, and resistorsR4, R5, and R6. The n-type transistors M6 and M7 are formed in thep-type well of the n-type substrate, and have the same impurityconcentration of the substrate and the channel dope regions. Theelectric potential of the substrate of each transistor is equal to thesource potential. The n-type transistor M6 has a highly-doped n-typegate, while the n-type transistor M7 has a highly-doped p-type gate. Theratios (W/L) of the channel width W to the channel length L of thetransistors M6 and M7 are set equal to each other.

[0119] The pair of transistors M6 and M7, which are the substantiallysame except for the gate polarities, function as input transistors of adifferential amplifier. The p-type transistors M4 and M5 form acurrent-mirror circuit. The voltage Vptat′ is applied to the gate ofn-type transistor M6 from the first reference voltage generatingcircuit. The gate of n-type transistor M7 is connected to the firstreference voltage Vref, which is extracted from the drain of p-typetransistor M8 as the output of the differential amplifier.

[0120] Based on the first reference voltage Vref, the second and thirdreference voltages Tvref and Svref are produced through voltageconversion using resistors R4, R5, and R6. The second reference voltageTvref is output from the junction point between resistors R4 and R5, andsupplied to the comparison circuit. The third reference voltage Svref isoutput from the junction point between resistors R5 and R6, and suppliedto the subtraction circuit.

[0121] The subtraction circuit includes operational amplifiers OP1 andOP2, and resistors R7, R8, R9, and R10. The output Svref′ of theoperational amplifier OP1 is connected to the inversion input of theoperational amplifier OP1 itself, while the non-inversion input of theoperational amplifier receives the third reference voltage Svrefsupplied from the second reference voltage generating circuit. Theoutput Svref′ of the operational amplifier OP1 is supplied via resistorR7 to the inversion input of the operational amplifier OP2. The outputTvptat of the operational amplifier OP2 itself is also connected viaresistor R8 to the inversion input of the operational amplifier OP2. Onthe other hand, the non-inversion input of the operational amplifier OP2receives Svptat from the first voltage generating circuit via resistorR9. The non-inversion input of the operational amplifier OP2 is alsoconnected via resistor R10 to the ground voltage GND. The output Tvptatfrom the second operational amplifier OP2 becomes the output of thesubtraction circuit, and is supplied to the comparison circuit.

[0122] The comparison circuit comprises an operational amplifier OP3.The second reference voltage Tvref generated by the second referencevoltage generating circuit-is input to the inversion input of theoperational amplifier OP3, and Tvptat supplied from the subtractioncircuit is input to the non-inversion input of the operational amplifierOP3. The output Tout of the third operational amplifier OP3 is a finaloutput of the temperature sensor.

[0123]FIGS. 14A through 14D illustrate the temperature characteristicsof the output signals generated in the temperature sensor shown in FIG.13. The operation of the circuit shown in FIG. 13 will be explained withreference to these graphs.

[0124] Since the first voltage generating circuit uses adiode-connection of the NPN transistor, a voltage Svptat having anegative temperature coefficient (or slope) is generated in proportionto the absolute temperature, as illustrated in FIG. 14A.

[0125] Concerning the second voltage generating circuit, the n-typetransistor M1 with its gate coupled to its source is used as aconstant-current source, and two n-type transistors M1 and M2 areconnected in series in the first reference voltage generating circuit.Since the same quantity of electric current flows through transistors M1and M2 that have the gates of the same conductivity type but withdifferent impurity concentrations, the, potential difference between thesource-gate voltage of transistor M1 and the source-gate voltage oftransistor M2 becomes a PTAT voltage (Vptat) having a positivetemperature coefficient.

[0126] Since the gate of transistor M1 is coupled to its source, thereis no potential difference between the source and the gate. Therefore,the source-gate voltage of transistor M2 becomes the PTAT voltage(Vptat). From this Vptat, Vptat′ that is to be supplied to the secondreference vltage generating circuit is produced through a voltagedivider consisting of resistors R2 and R3. Vptat′ is expressed as

Vptat′=Vptat*(R 2+R 3)/R 3.   (7)

[0127] Since Vptat has a positive temperature coefficient, Vptat′ alsohas a positive temperature coefficient.

[0128] In the second reference voltage generating circuit, p-typetransistors M4 and M5 form a current mirror circuit, and n-typetransistors M6 and M7 with opposite gate polarities function as inputtransistors of the differential amplifier. Accordingly, the samequantity of electric current flows through the n-type transistors M6 andM7. In addition, because the differential amplifier (M6 and M7) andp-type transistor M8 form a feedback loop, an input offset Vpn having anegative temperature coefficient appears between the source-gate voltageof n-type transistor M6 and the source-gate voltage of n-type transistorM7, as described in U.S. Pat. No. 6,437,550.

[0129] When Vptat′ is applied to the gate of transistor M6 from thefirst reference voltage generating circuit, the first reference voltageVref, which is the sum of Vptat′ and Vpn, is generated between thesource and the gate of the n-type transistor M7. Since Vref is obtainedby adding Vpn having a negative temperature coefficient to Vptat′obtained from Vptat through the voltage-divider at a predeterminedratio, the resultant Vref does not have a temperature coefficient. Basedon the first reference voltage Vref, the second and third referencevoltages Tvref and Sverf are generated through the voltage divider usingresistors R4, R5 and R6. The reference voltages Vref, Tvref, and Svrefare expressed by equations (8), (9), and (10).

Vref=Vptat*(R 2+R 3)/R 3+Vpn=Vptat′+Vpn   (8)

Tvref=Vref*(R 5+R 6)/(R 4+R 5+R 6)   (9)

Svref=Vref*R 6/(R 4+R 5+R 6)   (10)

[0130]FIG. 14B exhibits the characteristics of these reference voltages.As shown in the graph, the first reference voltage Vref is generated byadding Vptat′, which has a positive temperature coefficient and issupplied from the first reference voltage generating circuit, to Vpn,which has a negative temperature coefficient and is generated in thesecond reference voltage generating circuit. The second and thirdreference voltages Tvref and Svref are generated by converting Vref atpredetermined ratios defined by equation (9) and (10), respectively.Consequently, both Tvref and Svref are constant without having atemperature coefficient.

[0131]FIG. 14C shows the temperature characteristics of voltagesproduced in the subtraction circuit, which includes operationalamplifiers OP1 and OP2, and resistors R7, R8, R9, and R10. Since theoperational amplifier OP1 is used as a voltage follower, an Svref′,which has the same potential as the third reference voltage Svrefsupplied to the non-inversion input of OP1, is obtained from theoperational amplifier OP1. The operational amplifier OP1 is inserted forthe purpose of preventing an electric current path from being producedbetween Tvptat (output of the operational amplifier Op2) and the thirdreference voltage Svref via resistors R8, R7, and R6, because such anelectric current path causes the reference voltages produced in thesecond voltage generating circuit to fluctuate.

[0132] The operational amplifier OP2 is used as a differentialamplifier. By setting R7 equal to R9 (R7=R9) and setting R8 equal to R10(R8=R10), the output Tvptat of the operational amplifier OP2 becomes

Tvptat=(R 8/R 7)*(Svptat−Svref′)   (11)

[0133] as is known in the art. When the temperature is lower than T1,Svptat is greater than Svref (Svptat>Svref), and therefore, equation(11) applies. The subtraction result of (Svptat-Svref′) of theright-hand side of equation (11) is illustrated as the dotted line A inFIG. 14C. This subtraction result is amplified by resistors R8 and R7 toobtain Tvptat. On the other hand, if the temperature is higher than T1,Svptat is smaller than Svref (Svptat<Svref), and the subtraction resultis treated as 0 volts. Consequently, even if the ratio R8 to R7 (R8/R7)is increased, which means, even if the slope or the temperaturecoefficient of Tvptat is increased, for the purpose of improving thesensitivity to realize a highly precise temperature sensor, low-voltageoperation is guaranteed because the Tvptat is reduced by a voltagecorresponding to Svref′ that equals the third reference voltage Svref.

[0134]FIG. 14D shows the temperature characteristics of the signalstreated in the comparison circuit. The comparison circuit is comprisedof operational amplifier OP3. The operational amplifier OP3 is used as acomparator. If the temperature is lower than T, Tvref is smaller thanTvptat (Tvref<Tvptat). Because the voltage at the non-inversion input ishigher than that of the inversion input, the output Tout of thecomparator is High. When the temperature is higher than T, then Tvrefbecomes greater than Tvptat (Tvref>Tvptat). Since the voltage at theinversion input is greater than that of the non-inversion input, theoutput Tout of the comparator becomes Low.

[0135] By using the output Tout as a control signal for a semiconductorintegrated circuit, the operation of the semiconductor integratedcircuit can be correctly stopped at a predetermined temperature T, whileallowing the temperature sensor to operate at a low voltage. The firstreference signal Vref is output externally from the temperature sensor,which may be used in the semiconductor integrated circuit.

[0136]FIG. 15 is a circuit diagram of a modification of the temperaturesensor shown in FIG. 12. This circuit is formed in an n-type substrate.In this modification, a PTAT voltage (Vptat) having a positivetemperature coefficient is generated from the first voltage generatingcircuit. Both the first and second voltage generating circuits make useof the principle of difference in gate work function disclosed in U.S.Pat. No. 6,437,550.

[0137] The first voltage generating circuit comprises n-type transistorsM11, M12, and M13, and resistors R12 and R13. Transistors M11 and M12are formed in the p-type well of the n-type substrate, and have the sameimpurity concentration at the channel regions and the source/drainregions. The electric potential of the substrate of each transistor isequal to the source potential. The n-type transistor M11 has ahighly-doped n-type gate, and the n-type transistor M12 has alightly-doped n-type gate. The ratios (W/L) of the channel width W tothe channel length L of the transistors M11 and M12 are set equal toeach other.

[0138] Transistors M11 and M12, which are substantially the same exceptfor the impurity concentrations of the gates, are connected in series.The gate of n-type transistor M11 is coupled to its source. Thistransistor M11 is used as a constant-current source. The n-typetransistor M12 is furnished with a gate voltage by a source followercomprised of an n-type transistor M13 and resistors R12 and R13. ThePTAT voltage (Vptat) is output from the junction point between the gateof n-type transistor M12 and resistors R12 and R13. Another voltageSvptat is output from the junction point between the source of n-typetransistor M13 and resistor R12.

[0139] The second voltage generating circuit is comprised of a firstreference voltage generating circuit and a second reference voltagegenerating circuit. The first reference voltage generating circuitincludes n-type transistors M1, M2, and M3, and resistors R2 and R3. Then-type transistors M1 and M2 are formed in the p-well of the n-typesubstrate, and have the same impurity concentration at the substrate andchannel dope regions. The substrate potential of each transistor isequal to its source voltage. The n-type transistor M1 has a highly-dopedn-type gate, and n-type transistor M2 has a highly-doped p-type gate.The ratios (W/L) of the channel width W to the channel length L of thesetwo transistors are equal to each other.

[0140] The n-type transistors M1 and M2, which are substantially thesame except for the polarity of the gate, are connected in series. Thegate of n-type transistor M1 is coupled to its source. This transistorM1 is used as a constant-current source. N-type transistor M2 has a gatevoltage defined by the source follower formed by n-type transistor M3and resistors R2 and R3. A voltage Vpn having a negative temperaturecoefficient is extracted from the junction point between the gate ofn-type transistor M2 and the source of n-type transistor M3. A voltageVpn′ is extracted from the junction point between resistors R2 and R3.

[0141] The second reference voltage generating circuit comprises p-typetransistors M4, M5, and M8, n-type transistors M6 and M7, and resistorsR4, R5, and R6. The n-type transistors M6 and M7 are formed in thep-type well of the n-type substrate, and have the same impurityconcentration of the substrate and the channel dope regions. Theelectric potential of the substrate of each transistor is equal to thesource potential. The n-type transistor M6 has a highly-doped n-typegate, while the n-type transistor M7 has a lightly-doped n-type gate.The ratios (W/L) of the channel width W to the channel length L of thetransistors M6 and M7 are set equal to each other.

[0142] The n-type transistors M6 and M7, which are the substantiallysame except for the impurity concentrations of the gates, function asinput transistors of a differential amplifier. The p-type transistors M4and M5 form a current-mirror circuit. The voltage Vpn′ is applied to thegate of n-type transistor M6 from the first reference voltage generatingcircuit. The gate of n-type transistor M7 is connected to the drain ofp-type transistor M8, and accordingly, to the first reference voltageVref extracted from the drain of transistor M8 as the output of thedifferential amplifier.

[0143] Based on the first reference voltage Vref, the second and thirdreference voltages Tvref and Svref are produced through thevoltage-divider using resistors R4, R5, and R6. The second referencevoltage Tvref is output from the junction point between resistors R4 andR5, and supplied to the comparison circuit. The third reference voltageSvref is output from the junction point between resistors R5 and R6, andsupplied to the subtraction circuit.

[0144] The subtraction circuit includes operational amplifiers OP1 andOP2, and resistors R7, R8, R9, and R10. The output Svref′ of theoperational amplifier OP1 is connected to the inversion input of theoperational amplifier OP1 itself, while the non-inversion input of theoperational amplifier receives the third reference voltage Strefsupplied from the second reference voltage generating circuit. Theoutput Svref′ of the operational amplifier OP1 is supplied via resistorR7 to the inversion input of the operational amplifier OP2. The outputTvptat of the operational amplifier OP2 itself is also connected viaresistor R8 to the inversion input of the operational amplifier OP2. Onthe other hand, the non-inversion input of the operational amplifier OP2receives Svptat from the first voltage generating circuit via resistorR9. The non-inversion input of the operational amplifier OP2 is alsoconnected via resistor R10 to the ground voltage GND.

[0145] The comparison circuit comprises an operational amplifier OP3.The second reference voltage Tvref generated by the second referencevoltage generating circuit is input to the inversion input of theoperational amplifier OP3, while Tvptat supplied from the subtractioncircuit is input to the non-inversion input of the operational amplifierOP3. The output Tout of the third operational amplifier OP3 is a finaloutput of the temperature sensor.

[0146]FIGS. 16A through 16D illustrate the temperature characteristicsof the output signals generated in the temperature sensor shown in FIG.15, and the operations of the circuits shown in FIG. 15 will beexplained based on these figures.

[0147] In the first voltage generating circuit, the n-type transistorM11 with the gate coupled to its source is used as a constant-currentsource, and n-type transistors M11 and M12 are connected in series.Since the same quantity of electric current flows through transistorsM11 and M12 that have the same conductivity (n-type), but with differentimpurity concentrations of the gate, the potential difference betweenthe source-gate voltage of n-type transistor M11 and the source-gatevoltage of n-type transistor M12 becomes a PTAT voltage (Vptat) having apositive temperature coefficient, as disclosed in U.S. Pat. No.6,437,550.

[0148] Since the gate of the n-type transistor M11 is coupled to itssource, there is no potential difference between the gate and thesource. Consequently, the source-gate voltage of the n-type transistorM12 becomes Vptat. Then, Svptat, which is the output of the firstvoltage generating circuit, becomes

Svptat=Vptat*(R 12+R 13)/R 13.   (12)

[0149]FIG. 16A shows the temperature characteristics of voltages Vptatand Svptat. Vptat is amplified at the ratio defined by equation (12) soas to produce Svptat. Because Vptat has a positive temperaturecoefficient, Svptat also has a positive temperature coefficient. Svptatdoes not have to have such a large slope as Tvptat2 shown in FIG. 11.

[0150] Concerning the second voltage generating circuit, the n-typetransistor M1 with its gate coupled to its source is used as aconstant-current source, and two n-type transistors M1 and M2 areconnected in series in the first reference voltage generating circuit.Since the same quantity of electric current flows through transistors M1and M2 that have the same conductivity and different gate polarities,the potential difference between the source-gate voltage of transistorM1 and the source-gate voltage of transistor M2 becomes a voltage havinga negative temperature coefficient, which is referred to as Vpn. Becausethe gate of transistor M1 is coupled to its source, there is nopotential difference between the source and the gate of this transistor.Therefore, the source-gate voltage of transistor M2 becomes the Vpnvoltage.

[0151] From this voltage Vpn, Vpn′ is produced as the output of thefirst reference voltage generating circuit, by converting Vpn at apredetermined ratio defined by equation (12)

Vpn′=Vpn*R 3/(R 2+R 3)   (13)

[0152] Since Vpn has a negative temperature coefficient, Vpn′ also has apositive temperature coefficient.

[0153] In the second reference voltage generating circuit, p-typetransistors M4 and M5 form a current mirror circuit, and n-typetransistors M6 and M7 having difference gate impurity concentrationsfunction as input transistors of the differential amplifier.Accordingly, the same quantity of electric current flows through then-type transistors M6 and M7. In addition, because a feedback loop isformed by the differential amplifier (M6 and M7) and p-type transistorM8, an input offset Vptat having a positive temperature coefficientappears between the source-gate voltage of n-type transistor M6 and thesource-gate voltage of n-type transistor M7, as described in U.S. Pat.No. 6,437,550.

[0154] When Vpn′ is applied to the gate of transistor M6 from the firstreference voltage generating circuit, the first reference voltage Vref,which is the sum of Vpn′ and Vptat, is generated between the source andthe gate of the n-type transistor M7. Since Vref is obtained by addingVptat having a positive temperature coefficient to Vpn′ obtained throughvoltage conversion at a predetermined ratio based on Vpn, the resultantVref does not have a temperature coefficient. Based on the firstreference voltage Vref, the second and third reference voltages Tvrefand Sverf are generated through the voltage divider using resistors R4,R5 and R6. The reference voltages Vref, Tvref, and Svref are expressedby equations (13), (9), and (10).

Vref=Vpn*R 3/(R 2+R 3)+Vptat=Vpn′+Vpn   (14)

Tvref=Vref*(R 5+R 6)/(R 4+R 5+R 6)   (9)

Svref=Vref*R 6/(R 4+R 5+R 6)   (10)

[0155]FIG. 16B exhibits the temperature characteristics of thesereference voltages, as well as Vpn and Vptat. The first referencevoltage Vref is generated by adding Vpn′, which has a negativetemperature coefficient and is supplied from the first reference voltagegenerating circuit, to Vptat, which has a positive temperaturecoefficient and is generated in the second reference voltage generatingcircuit. The second and third reference voltages Tvref and Svref aregenerated from Vref, through voltage conversion at predetermined ratiosdefined by equation (9) and (10), respectively. Consequently, both Tvrefand Svref are constant without having a temperature coefficient.

[0156]FIG. 16C shows the temperature characteristic of voltages treatedin the subtraction circuit, which includes operational amplifiers OP1and OP2, and resistors R7, R8, R9, and R10. Since the operationalamplifier OP1 is used as a voltage follower, an output Svref′, which hasthe same potential as the third reference voltage Svref supplied to thenon-inversion input of OP1 is obtained from the operational amplifierOP1. The operational amplifier OP1 is inserted for the purpose ofpreventing an electric current path from being produced between Tvptat(output of the operational amplifier Op2) and the third referencevoltage Svref via resistors R8, R7, and R6, because such an electriccurrent path causes the reference voltages produced in the secondvoltage generating circuit to fluctuate.

[0157] The operational amplifier OP2 is used as a differentialamplifier. By setting R7 equal to R9 (R7=R9) and setting R8 equal to R10(R8=R10), the output Tvptat of the operational amplifier OP2 becomes

Tvptat=(R 8/R 7)*(Svptat−Svref′)   (11)

[0158] as is known in the art. When the temperature is lower than T1,Svref is greater than Svptat (Svptat<Svref), the subtraction result istreated as 0 volts. If the temperature is higher than T1, Svptat isgreater than Svref (Svptat>Svref), and therefore, equation (11) applies.The subtraction result of (Svptat−Svref′) of the right-hand side ofequation (11) is illustrated as the dotted line A in FIG. 16C. Thissubtraction result is amplified by resistors R8 and R7 to obtain Tvptat.From equations (11) and (12), the ratio S of the temperature coefficient(or the slope) of Tvptat to that of Vptat is expressed as

S=[(R 12+R 13)/R 13]*R 8/R 7.   (15)

[0159] By simply adjusting the resistances R12, R13, R7 and R8, theratio S defined by equation (14) can be easily made equal to the ratio(R1+R2+R5)/R5, which is the temperature coefficient of Tvptat obtainedin the first embodiment. For instance, if the temperature coefficient ofTvptat generated in the first voltage generating circuit shown in FIG. 4is fifty (50), the temperature coefficient ratio (R12+R13)/R13 definedin the first voltage generating circuit of the second embodiment is setto 10, and the temperature coefficient ratio R8/R7 defined in thesubtraction circuit is set to 5. By so setting, the ratio S (that is,the temperature coefficient ratio of Tvptat) becomes fifty (50), as inthe circuit disclosed in the first embodiment. This means that the firstvoltage generating circuit of the second embodiment does not have toproduce Tvptat having a large slope (or the temperature coefficientratio) by itself.

[0160]FIG. 16D shows the temperature characteristics of the voltagestreated in the comparison circuit. The comparison circuit is comprisedof operational amplifier OP3. The operational amplifier OP3 is used as acomparator. If the temperature is lower than T, Tvref is greater thanTvptat (Tvref>Tvptat). Because the voltage at the inversion input ishigher than that of the non-inversion input, the output Tout of thecomparator is Low. When the temperature is higher than T, then Tvrefbecomes smaller than Tvptat (Tvref<Tvptat). Since the voltage at thenon-inversion input is greater than that of the non-inversion input, theoutput Tout of the comparator becomes High. The output Tout is used as acontrol signal for controlling the operation of a semiconductorintegrated circuit so as to stop at a predetermined temperature T.

[0161] In the second embodiment, the first voltage generating circuituses either a diode connection of NPN transistor or the principle ofdifference in gate work function to produce a PTAT voltage. However, thepresent invention is not limited to these examples, and any othersuitable circuit configuration can be employed as the first voltagegenerating circuit, as long as a PTAT voltage is generated. Similarly,although, in the second embodiment, the second voltage generatingcircuit uses the principle of difference in gate work function toproduce a reference voltage, any other suitable circuit, such as aband-gap reference circuit, may be used to as the second voltagegenerating circuit.

[0162] <Third Embodiment>

[0163]FIG. 17 is a block diagram of the temperature sensor according tothe third embodiment of the invention. The temperature sensor comprisesa first voltage generating circuit, a second voltage generating circuit,a subtraction circuit, and a comparison circuit, as in the secondembodiment. In the third embodiment, a voltage Vptat′ is output from thefirst voltage generating circuit, and supplied to the second voltagegenerating circuit. This Vptat′ is used in the second generating voltagecircuit to produce a reference voltage.

[0164] The first voltage generating circuit also outputs Svptat, inadiition to Vptat′. The Svptat and Vptat′ are produced from a PTATvoltage (not shown in FIG. 17) originally generated in the first voltagegenerating circuit in proportion to the absolute temperature, throughvoltage conversion at predetermined ratios using a voltage divider. Inthe second embodiment, the PTAT voltage, Svptat, and Vptat′ havepositive temperature coefficients.

[0165] The second voltage generating circuit generates a voltage havinga negative temperature coefficient (not shown in FIG. 17), and adds thisvoltage to Vptat′ supplied from the first voltage generating circuit toproduce the first reference voltage Vref that does not have atemperature coefficient. The second voltage generating circuit alsooutputs the second reference voltage Tvref and the third referencevoltage Svref, which are produced from Vref and do not have atemperature coefficient.

[0166] The subtraction circuit amplifies the difference between Svptatsupplied from the first voltage generating circuit and the thirdreference voltage Svref supplied from the second voltage generatingcircuit, and produces a voltage Tvptat.

[0167] The comparison circuit compares the Tvptat with the secondreference voltage Tvref, and outputs the comparison result Tout.

[0168] If the first voltage generating circuit is designed so as toproduce a voltage with a negative temperature coefficient, then avoltage with a negative temperature coefficient is generated in thesecond voltage generating circuit to produce the reference voltages.Both the first and second voltage generating circuits make use of theprinciple of difference in gate work function.

[0169]FIG. 18 is a circuit diagram of the temperature sensor shown inFIG. 17. This circuit is fabricated in an n-type substrate.

[0170] The first voltage generating circuit comprises n-type transistorsM1, M2, and M3, and resistors R1, R2 and R3. Transistors M1 and M2 areformed in the p-type well of the n-type substrate, and have the sameimpurity concentration at the channel regions and the source/drainregions. The electric potential of the substrate of each transistor isequal to the source potential. The n-type transistor M1 has ahighly-doped n-type gate, and n-type transistor M2 has a lightly-dopedn-type gate. The ratios (W/L) of the channel width W to the channellength L of the transistors M1 and M2 are set equal to each other.

[0171] The transistors M1 and M2, which are substantially the sameexcept for the impurity concentrations of the gates, are connected inseries. The gate of transistor M1 is coupled to its source. Thus, thetransistor M1 is used as a constant-current source. The gate potentialof the n-type transistor M2 is given by the source follower formed byn-type transistor M3 and resistors R1, R2, and R3. While Vptat isextracted from the junction point between resistors R2 and R3, Vptat′ isoutput from the junction point between resistors R1 and R2. Anothervoltage Svptat is output from the junction point between the source oftransistor M3 and resistor R1.

[0172] The second voltage generating circuit comprises p-typetransistors M4, M5, and M8, n-type transistors M6 and M7, and resistorsR4, R5, and R6. The n-type transistors M6 and M7 are formed in thep-type well of the n-type substrate, and have the same impurityconcentration of the substrate and the channel dope regions. Theelectric potential of the substrate of each transistor is equal to thesource potential. The n-type transistor M6 has a highly-doped n-typegate, and n-type transistor M7 has a highly-doped p-type gate. Theratios (W/L) of the channel width W to the channel length L of thetransistors M6 and M7 are set equal.

[0173] The n-type transistors M6 and M7, which are substantially thesame except for the gate polarities, function as input transistors of adifferential amplifier. The p-type transistors M4 and M5 form acurrent-mirror circuit. The voltage Vptat′ output from the first voltagegenerating circuit is applied to the gate of n-type transistor M6. Thegate of n-type transistor M7 is connected to the first reference voltageVref, which is extracted from the drain of the p-type transistor M8 andis the output of the differential amplifier. The first reference Vref isdivided by resistors R4, R5, and R6 to produce the second and thirdreference voltages. The second reference voltage Tvref is output fromthe junction point between resistors R4 and R5. The third referencevoltage Svref is output from the junction point from resistors R5 andR6.

[0174] The subtraction circuit includes operational amplifiers OP1 andOP2, and resistors R7, R8, R9, and R10. The output Svref′ of theoperational amplifier OP1 is connected to the inversion input of theoperational amplifier OP1 itself, while the non-inversion input of theoperational amplifier receives the third reference voltage Strefsupplied from the second voltage generating circuit. The output Svref′of the operational amplifier OP1 is supplied via resistor R7 to theinversion input of the operational amplifier OP2. The output Tvptat ofthe operational amplifier OP2 itself is also connected via resistor R8to the inversion input of the operational amplifier OP2. On the otherhand, the non-inversion input of the operational amplifier OP2 receivesSvptat from the first voltage generating circuit via resistor R9. Thenon-inversion input of the operational amplifier OP2 is, also connectedvia resistor R10 to the ground voltage GND.

[0175] The comparison circuit comprises an operational amplifier OP3.The second reference voltage Tvref is input from the second voltagegenerating circuit to the inversion input of the operational amplifierOP3, while Tvptat is input from the subtraction circuit to thenon-inversion input of the operational amplifier OP3. The output Tout ofthe third operational amplifier OP3 is a final output of the temperaturesensor.

[0176]FIGS. 19A through 19D illustrate the output characteristics of thetemperature sensor shown in FIG. 18, and the operations of the circuitsshown in FIG. 18 will be explained using-these figures.

[0177] In the first voltage generating circuit, the n-type transistor M1with the gate coupled to its source is used as a constant-currentsource, and n-type transistors M1 and M2 are connected in series. Sincethe same quantity of electric current flows through transistors M1 andM2 that have the same conductivity (n-type), but with different impurityconcentrations of the gates, the potential difference between thesource-gate voltage of n-type transistor M1 and the source-gate voltageof n-type transistor M2 becomes a PTAT voltage (Vptat) having a positivetemperature coefficient, as disclosed in U.S. Pat. No. 6,437,550.

[0178] Because the gate of the n-type transistor M1 is coupled itssource, there is no potential difference between the gate and thesource. Consequently, the source-gate voltage of the n-type transistorM2 becomes Vptat. Then, the outputs Vptat′ and Svptat of the firstvoltage generating circuit become

Vptat′=Vptat*(R 2+R 3)/R 3   (7)

Svptat=Vptat*(R 1+R 2+R 3)/R 3.   (16)

[0179]FIG. 19A shows the temperature characteristics of these voltages.Vptat′ and Svptat are produced by amplifying Vptat at predeterminedratios defined in equations (7) and (16). Because Vptat has a positivetemperature coefficient, Vptat′ and Svptat also have positivetemperature coefficients. This Svptat does not have to have such a largeslope as Tvptat2 shown in FIG. 11.

[0180] Concerning the second voltage generating circuit, p-typetransistors M4 and M5 form a current mirror circuit, and n-typetransistors M6 and M7 having difference gate polarities function asinput transistors of the differential amplifier. Accordingly, the samequantity of electric current flows through the n-type transistors M6 andM7. In addition, because a feedback loop is formed by the differentialamplifier (M6 and M7) and p-type transistor M8, an input offset Vpnhaving a negative temperature coefficient appears between thesource-gate voltage of n-type transistor M6 and the source-gate voltageof n-type transistor M7.

[0181] When Vptat′ is applied to the gate of the n-type transistor M6from the first voltage generating circuit, the first reference voltageVref, which is the sum of Vpn and Vptat′, appears between the source andthe gate of the n-type transistor M7. Since Vref is obtained by addingVpn having a negative temperature coefficient to Vptat′ having apositive temperature coefficient, which is obtained from Vptat throughvoltage conversion at a predetermined ratio, the resultant Vref does nothave a temperature coefficient. Based on the first reference voltageVref, the second and third reference voltages Tvref and Sverf aregenerated through the voltage divider using resistors R4, R5 and R6. Thereference voltages Vref, Tvref, and Svref are expressed by equations(8), (9), and (10).

Vref=Vptat*(R 2+R 3)/R 3+Vpn=Vptat′+Vpn   (8)

Tvref=Vref*(R 5+R 6)/(R 4+R 5+R 6)   (9)

Svref=Vref*R 6/(R 4+R 5+R 6)   (10)

[0182]FIG. 19B exhibits the temperature characteristics of thesereference voltages. As shown in the graph, the first reference voltageVref is generated by adding Vptat′, which has a positive temperaturecoefficient and is supplied from the first voltage generating circuit,to Vpn, which has a negative temperature coefficient and is generated inthe second voltage generating circuit. The second and third referencevoltages Tvref and Svref are generated by converting Vref atpredetermined ratios defined by equation (9) and (10), respectively.Consequently, both Tvref and Svref are constant without having atemperature coefficient.

[0183]FIG. 19C shows the temperature characteristics of voltagesproduced in the subtraction circuit, which includes operationalamplifiers OP1 and OP2, and resistors R7, R8, R9, and R10. Since theoperational amplifier OP1 is used as a voltage follower, an Svref′,which has the same potential as the third reference voltage Svref inputto the non-inversion input of OP1, is obtained from the operationalamplifier OP1. The operational amplifier OP1 is inserted for the purposeof preventing an electric current path from being produced betweenTvptat (output of the operational amplifier Op2) and the third referencevoltage Svref via resistors R8, R7, and R6, because such an electriccurrent path causes the reference voltages produced in the secondvoltage generating circuit to fluctuate.

[0184] The operational amplifier OP2 is used as a differentialamplifier. By setting R7 equal to R9 (R7=R9) and setting R8 equal to R10(R8=R10), the output Tvptat of the operational amplifier OP2 becomes

Tvptat=(R 8/R 7)*(Svptat−Svref′)   (11)

[0185] as is known in the art. When the temperature is lower than T1,Svptat is smaller than Svref (Svptat<Svref), and in this case, theoutput Tvptat of the subtraction circuit is 0 volts. If the temperatureis higher than T1, Svptat>Svref stands, and a voltage defined byequation (11) is output. From equations (11) and (16), the ratio S ofthe temperature coefficient (or the slope) of Tvptat to that of Vptat isexpressed as

S=[(R 1+R 2+R 3)/R 3]*R 8/R 7.   (17)

[0186] By simply adjusting the resistances R1 through R3, and R7 and R8,the ratio S defined by equation (17) can be easily made equal to theratio (R1+R2+R5)/R5, which is, the temperature coefficient of Tvptatobtained in the first embodiment.

[0187] For instance, if the temperature coefficient of Tvptat generatedin the first voltage generating circuit shown in FIG. 4 is fifty (50),the temperature coefficient ratio (R1+R2+R3)/R3] defined in the firstvoltage generating circuit of the third embodiment is set to 10, and thetemperature coefficient ratio R8/R7 defined in the subtraction circuitis set to 5. By so setting, the ratio S (that is, the temperaturecoefficient ratio of Tvptat) becomes fifty (50), as in the circuitdisclosed in the first embodiment. This means that it is unnecessary forthe first voltage generating circuit of the third embodiment to produceTvptat having a large slope (or the temperature coefficient ratio) byitself.

[0188]FIG. 19D shows the temperature characteristics of the signalstreated in the comparison circuit. The comparison circuit is comprisedof operational amplifier OP3. The operational amplifier OP3 is used as acomparator. If the temperature is lower than T, Tvref>Tvptat stands.Because the voltage at the inversion input is higher than that of thenon-inversion input, the output Tout of the comparator is Low. When thetemperature is higher than T, then Tvref<Tvptat stands. Since thevoltage at the non-inversion input is greater than that of the inversioninput, the output Tout of the comparator becomes High. By using theoutput Tout as a control signal for a semiconductor integrated circuit,the operation of the semiconductor integrated circuit can be correctlystopped at a predetermined temperature T, while allowing the temperaturesensor to operate at a low voltage.

[0189]FIG. 20 is a circuit diagram of a modification of the temperaturesensor according to the third embodiment of the invention. This circuitis fabricated in an n-type substrate.

[0190] The first voltage generating circuit comprises n-type transistorsM1, M2, and M3, and resistors R1, R2 and R3. Transistors M1 and M2 areformed-in the p-type well of the n-type substrate, and have the sameimpurity concentration at the channel regions and the source/drainregions. The electric potential of the substrate of each transistor isequal to the source potential. The n-type transistor M1 has ahighly-doped n-type gate, and n-type transistor M2 has a lightly-dopedn-type gate. The ratios (W/L) of the channel width W to the channellength L of the transistors M1 and M2 are set equal to each other.

[0191] The transistors M1 and M2, which are substantially the sameexcept for the impurity concentrations of the gates, are connected inseries. The gate of transistor M1 is coupled to its source. Thus, thetransistor M1 is used as a constant-current source. The gate potentialof the n-type transistor M2 is given by the source follower formed byn-type transistor M3 and resistors R1, R2, and R3. While Vptat isextracted from the junction point between resistors R2 and R3, Vptat′ isoutput from the junction point between resistors R1 and R2. Anothervoltage Svptat is output from the junction point between the source oftransistor M3 and resistor R1.

[0192] The second voltage generating circuit, comprises p-typetransistors M4, M5, and M8, n-type transistors M6 and M7, and resistorsR4, R5, and R6. The n-type transistors M6 and M7 are formed in thep-type well of the n-type substrate, and have the same impurityconcentration of the substrate and the channel dope regions. Theelectric potential of the substrate of each transistor is equal to thesource potential. The n-type transistor M6 has a highly-doped n-typegate, and n-type transistor M7 has a highly-doped p-type gate. Theratios (W/L) of the channel width W to the channel length L of thetransistors M6 and M7 are set equal to each other.

[0193] The n-type transistors M6 and M7, which are substantially thesame except for the gate polarities, function as input transistors of adifferential amplifier. The p-type transistors M4 and M5 form acurrent-mirror circuit. The voltage Vptat′ output from the first voltagegenerating circuit is applied to the gate of n-type transistor M6. Thegate of n-type transistor M7 is connected to the first reference voltageVref, which is extracted from the drain of the p-type transistor M8 andis the output of the differential amplifier. The first reference Vref isdivided by resistors R4, R5, and R6 to produce the second and thirdreference voltages. The second reference voltage Tvref is output fromthe junction point between resistors R4 and R5. The third referencevoltage Svref is output from the junction point from resistors R5 andR6.

[0194] The subtraction circuit includes operational amplifier OP2, andresistors R7, R8, R9, and R10. The third reference voltage Svref isconnected via resistor R7 to the inversion input of the operationalamplifier OP2. The inversion input of the operational amplifier OP2 alsoreceives a voltage Tvpatat, which is the output of the operationalamplifier OP2 itself, via resistor R8. On the other hand, thenon-inversion input of the operational amplifier OP2 receives Svptatfrom the first voltage generating circuit via resistor R9. Thenon-inversion input of the operational amplifier OP2 is also connectedvia resistor R10 to the ground voltage GND.

[0195] The comparison circuit comprises an operational amplifier OP3.The second reference voltage Tvref is input from the second voltagegenerating circuit to the inversion input of the operational amplifierOP3, while Tvptat is input from the subtraction circuit to thenon-inversion input of the operational amplifier OP3. The output Tout ofthe third operational amplifier OP3 is a final output of the temperaturesensor.

[0196] In operation, since the first voltage generating circuit of thismodification is the same as that used in the circuit shown in FIG. 18, avoltage Vptat having a positive temperature coefficient, whichcorresponds to the source-gate voltage of n-type transistor M2, isoutput. The outputs Vptat′ and Svptat of the first voltage generatingcircuit are produced through voltage conversion using resistors R1, R2,and R3, as defined in equations (7) and (16).

Vptat′=Vptat*(R 2+R 3)/R 3   (7)

Svptat=Vptat*(R 1+R 2+R 3)/R 3.   (16)

[0197] These voltages generated in the first voltage generating circuithave positive temperature coefficients as illustrated in FIG. 19A.

[0198] The second voltage generating circuit of this modification isalso the same as that used in the circuit shown in FIG. 18. Accordingly,there is an input offset Vpn having a negative temperature coefficientbetween the source-gate voltage of n-type transistor M6 and thesource-gate voltage of n-type transistor M7. Since Vptat′ is applied tothe gate of the n-type transistor M6 from the first voltage generatingcircuit, the first reference voltage Vref, which is the sum of Vpn andVptat′ as expressed by equation (8), appears between the source and thegate of the n-type transistor M7. The second and third referencevoltages Tvref and Sverf are produced from the first reference voltageVref through the voltage divider using resistors R4, R5 and R6, asexpressed by equations (9) and (10).

Tvref=Vref*(R 5+R 6)/(R 4+R 5+R 6)   (9)

Svref=Vref*R 6/(R 4+R 5+R 6)   (10)

[0199] The temperature characteristics of these reference voltagesproduced in the second voltage generating circuit are illustrated inFIG. 19B.

[0200] The subtraction circuit of this modification is comprised ofoperational amplifier OP2, and resistors R7, R8, R9, and R10. Theoperational amplifier OP2 is used as a differential amplifier. Bysetting R7 equal to R9 (R7=R9) and setting R8 equal to R10 (R8=R10), theoutput Tvptat of the operational amplifier OP2 becomes

Tvptat=(R 8/R 7)*(Svptat−Svref′)   (11)

[0201] as is known in the art. When the temperature is lower than T1,Svptat<Svref stantds, Tvptat becomes 0 volts. If the temperature ishigher than T1, Svptat<Svref stands, and a voltage defined by equation(11) is output. From equations (11) and (16), the ratio S of thetemperature coefficient (or the slope) of Tvptat to that of Vptat isexpressed as

S=[(R 1+R 2+R 3)/R 3]*R 8/R 7.   (17)

[0202] By simply adjusting the resistances R1 through R3, and R7 and R8,the ratio S defined by equation (17) can be easily made equal to theratio (R1+R2+R5)/R5, which is the temperature coefficient of Tvptatobtained in the first embodiment.

[0203] For instance, if the temperature coefficient of Tvptat generatedin the first voltage generating circuit shown in FIG. 4 is fifty (50),the temperature coefficient ratio (R1+R2+R3)/R3] defined in the firstvoltage generating circuit of this modification is set to 10, and thetemperature coefficient ratio R8/R7 defined in the subtraction circuitis set to 5. By so setting, the ratio S (that is, the temperaturecoefficient ratio of Tvptat) becomes fifty (50), as in the circuitdisclosed in the first embodiment. This means that it is unnecessary forthe first voltage generating circuit of the third embodiment to produceTvptat having a large slope (or the temperature coefficient ratio) byitself.

[0204] Unlike the circuit shown in FIG. 18, operational amplifier OP1 isnot inserted before the operational amplifier OP2. Accordingly, anelectric current path may be created between Tvptat and the thirdreference voltage Svref via resistors R8, R7, and R6. To reduce theinfluence of the electric current path, the resistance values ofresistors T7 through R10 are set sufficiently larger than that ofresistor R6.

[0205] The comparison circuit is comprised of operational amplifier OP3.The operational amplifier OP3 is used as a comparator. If thetemperature is lower than T, Tvref>Tvptat stands. Because the voltage atthe inversion input is higher than that of the non-inversion input, theoutput Tout of the comparator is Low. When the temperature is higherthan T, then Tvref<Tvptat stands. Since the voltage at the non-inversioninput is greater than that of the inversion input, the output Tout ofthe comparator becomes High. By using the output Tout as a controlsignal for a semiconductor integrated circuit, the operation of thesemiconductor integrated circuit can be correctly stopped at apredetermined temperature T, while allowing the temperature sensor tooperate at a low voltage.

[0206]FIG. 21 is a graph showing the temperature characteristics ofTvptat used in the first, second, and third embodiments. In the firstembodiment, the temperature coefficient of Tvptat is converted to agreater value in the first voltage generating circuit in order toimprove the sensitivity of the temperature sensor, as illustrated inFIG. 11. The arrangement of the first embodiment causes Tvptat to becomehigh as the temperature rises, which may adversely affect the operatingvoltage of the circuit.

[0207] In contrast, in the second and third embodiment, the conversionratio of the first voltage generating circuit is not so large, ascompared with the circuit of the first embodiment. The first voltagegenerating circuit outputs Svptat produced at a smaller conversion(amplification) ratio. The subtraction circuit amplifies the differencebetween Svptat and the third reference voltage Svref to produce Tvptat.When Tvptat has a positive temperature coefficient, Tvptat can shiftlower with the temperature coefficient, as indicated by the arrow inFIG. 21. Consequently, the operation voltage of the temperatures sensorcan be reduced. If Tvptat has a negative temperature coefficient, theoutput voltage is also reduced with an opposite sign of temperaturecoefficient.

[0208] <Fourth Embodiment>

[0209]FIG. 22 is a block diagram of the temperature sensor according tothe fourth embodiment of the invention. The temperature sensor has twosets of subtraction circuits and comparison circuits. Two referencevoltages Svref1 and Svref2 are supplied from the second voltagegenerating circuit to the first and second subtraction circuits,respectively. Accordingly, two comparison results Tout 1 and Tout2 areoutput at different temperatures.

[0210]FIG. 23 is a circuit diagram of the temperature sensor shown inFIG. 22. The basic structure of the circuit shown in FIG. 23 is similarto the circuit shown in FIG. 13 of the second embodiment. The circuitshown in FIG. 23 has the first subtraction circuit and the firstcomparison circuit, which correspond to the subtraction circuit and thecomparison circuit shown in FIG. 13. The circuit of FIG. 23 also has asecond subtraction circuit and a second comparison circuit. The resistorR5 used in the second voltage generating circuit shown in FIG. 13 isdivided into resistors R5 a and R5 b in the fourth embodiment. Thereference voltage Svref1 is output from the junction point betweenresistors R6 and R5 b. The counterpart reference voltage Svref2 isoutput from the junction point between resistors R5 a and R5 b. Thereference voltage Svrer1 is supplied to the operational amplifier OP1 ofthe first subtraction circuit, and the reference voltage Svref2 issupplied to the operational amplifier OP11 of the second subtractioncircuit.

[0211]FIG. 24A through FIG. 24E illustrate the temperaturecharacteristics of the output voltages used in the temperature sensor ofthe fourth embodiment. The operation of the circuit shown in FIG. 23will be explained with reference to FIG. 24A through FIG. 24E.

[0212] The first voltage generating circuit uses a diode connection ofthe NPN transistor, as in the circuit shown in FIG. 13 (of the secondembodiment). Accordingly, it outputs Svptat that is a PTAT voltagehaving a negative temperature coefficient, as illustrated in FIG. 24A.

[0213] The second voltage generating circuit is similar to that shown inFIG. 13. Accordingly, when Vptat′ is applied to the gate of n-typetransistor M6 from the junction point between the source of transistorM3 and resistor R2, a voltage Vref that results from adding Vpn toVptat′ is generated between the source and the gate of the n-typetransistor M7. Since Vref is the sum of Vpn having a negativetemperature coefficient and Vptat′ having a positive temperaturecoefficient, which is obtained from Vptat through voltage conversion ata predetermined ratio, the resultant Vref (the first reference voltage)does not have a temperature coefficient. Based on the first referencevoltage Vref, the second reference voltage Tvref and two types of thirdreference voltages Sverf1 and Svref2 are generated through the voltageconversion using resistors R4, R5 a, R5 b, and R6. The referencevoltages Vref, Tvref, Svref1, and Svref are expressed by equations (8),(9), (10)′ and (10)″.

Vref=Vptat*(R 2+R 3)/R 3+Vpn=Vptat′+Vpn   (8)

Tvref=Vref*(R 5+R 6)/(R 4+R 5+R 6)   (9)

Svref1=Vref*R 6/(R 4+R 5 a+R 5 b+R 6)   (10)′

Svref2=Vref*(R 5 b+R 6)/(R 4+R 5 a+R 5 b+R 6)   (10)″

[0214]FIG. 24B illustrates the temperature characteristics of thesesignals.

[0215] The operation of the first subtraction circuit is the same as thesubtraction circuit shown in FIG. 13, but for that Svref1 is used inplace of Sverf. Accordingly, the output Tvptat1 of the operationalamplifier OP2 becomes

Tvptat1=(R 8/R 7)*(Svptat−Svref1′).   (11)′

[0216] The temperature characteristics of these signals are shown inFIG. 24C. The dotted line A1 indicates the subtraction result of(Svptat−Svref1′).

[0217] When the temperature is lower than T1, Svptat>Svref1 stands, andtherefore, equation (11)′ applies. If the temperature is higher than T1,Svptat<Svref1 stands, and the subtraction result is treated as 0 volts.Consequently, even if the ratio R8 to R7 (R8/R7) is increased, whichmeans, even if the slope or the temperature coefficient of Tvptat1 isincreased, for the purpose of improving the sensitivity to realize ahighly precise temperature sensor, low-voltage operation is guaranteedbecause the Tvptat1 is reduced by a voltage corresponding to Svref1′that equals the third reference voltage Svref1.

[0218] The same applies to the second subtraction circuit. The outputTvptat2 of the operational amplifier OP12 becomes

Tvptat2=(R 18/R 17)*(Svptat−Svref2′).   (11)″

[0219] The temperature characteristics of these signals are shown inFIG. 24D. The dotted line A2 indicates the subtraction result of(Svptat−Svref2′).

[0220] In the first comparison circuit, if the temperature is lower thanT1, Tvref<Tvptat1 stands, and output Tout1 of the comparator(operational amplifier OP3) becomes High. If the temperature is higherthan T1, Tvref>Tvptat1 stands, and therefore, the output Tout 1 becomesLow.

[0221] In the second comparison circuit, if the temperature is lowerthan T2, Tvref<Tvptat2 stands, and output Tout2 of the comparator(operational amplifier OP13) becomes High. If the temperature is higherthan T2, Tvref>Tvptat2 stands, and therefore the Tout2 becomes Low. Thetemperature characteristics of these signals are shown in FIG. 24E.

[0222] By using these outputs Tout1 and Tout 2 as control signals for asemiconductor integrated circuit, the operation of the semiconductorintegrated circuit can be controlled at two different temperatures T1and T2, as illustrated in FIG. 24E.

[0223] Three or more sets of subtraction circuits and comparisoncircuits may be used to produce three or more control signals.

[0224] Meanwhile, since using two sets of subtraction circuits andcomparison circuits increases the load on the circuit, a switchingdevice may be inserted between the second voltage generating circuit andthe subtraction circuit. In this case, Svref1 and Svref2 generated inthe second voltage generating circuit are switched and suppliedalternately to a single subtraction circuit. Then, a single comparisoncircuit outputs Tout1 and Tout2 alternately, at the respectivetemperatures. This arrangement is efficient because the semiconductorintegrated circuit can be controlled at two different temperatures witha single subtraction circuit.

[0225]FIG. 28 illustrates the temperatures characteristics of Tptat1 andTptat 2 generated in the fourth embodiment, as comparison with Tptatgenerated in the first embodiment. In order to improve the sensitivityof the temperature sensor of the first embodiment, the temperaturecoefficient of Tvptat is converted to a greater value in the firstvoltage generating circuit, as illustrated in FIG. 11. This arrangementcauses Tvptat to become high as the temperature rises, which mayadversely affect the operating voltage of the circuit.

[0226] In contrast, in the fourth embodiment, Svptat generated by thefirst voltage generating circuit is reduced to lower levels in twodifferent temperatures ranges by subtracting Svref1 and Svref2 by thefirst and second subtraction circuits, respectively. The subtractionresults are amplified to produce Tvpat1 and Tvpat2. These voltagesTvptat1 and Tvptat2 are smaller than Tvptat of the first embodiment byquantities of Svref1 and Sverf2, with temperature coefficients (orslopes) opposite to Tvptat. Consequently, the operating voltage of theentire temperature sensor can be reduced.

[0227] <Fifth Embodiment>

[0228]FIG. 25 is a block diagram of the temperature sensor according tothe fifth embodiment of the invention. This temperature sensor is acombination of the third and fourth embodiments. Namely, the outputVptat′ having a positive temperature coefficient is supplied to thesecond voltage generating circuit, which then generates two types ofthird reference signals Svref1 and Svref2. The signals Svref1 and Svref2are supplied to the first and second subtraction circuits, respectively.The first and second comparison circuits output Tout1 and Tout2,respectively, at different temperatures.

[0229]FIG. 26 is a circuit diagram of the temperature sensor shown inFIG. 25. The first and second voltage generating circuits of the fifthembodiment are the same as those shown in FIG. 18 of the thirdembodiment. The resistor R5 used in the second voltage generatingcircuit shown in FIG. 18 is divided into resistors R5 a and R5 b. Thereference voltage Svref1 is output from the junction point betweenresistors R6 and R5 b. The counterpart reference voltage Svref2 isoutput from the junction point between resistors R5 a and R5 b. Thereference voltage Svrer1 is supplied to the operational amplifier OP1 ofthe first subtraction circuit, and the reference voltage Svref2 issupplied to the operational amplifier OP11 of the second subtractioncircuit.

[0230]FIG. 27A through FIG. 27E show the temperature characteristics ofoutput signals generated in the circuit shown in FIG. 26, and theoperation of the circuit of FIG. 26 will be explained with reference tothese graphs. In the first voltage generating circuit, the source-gatevoltage of n-type transistor M2 becomes a PTAT voltage (Vptat) having apositive temperature coefficient. The outputs Vptat′ and Svptat of thefirst voltage generating circuit are expressed as

Vptat′=Vptat*(R 2+R 3)/R 3   (7)

Svptat=Vptat*(R 1+R 2+R 3)/R 3.   (16)

[0231]FIG. 27A illustrates the temperature characteristics of thesesignals generated in the first voltage generating circuit. Since Vptat′and Svptat are obtained from Vptat by voltage conversion at a prescribedratio defined by equations (7) and (16), Vptat′ and Svptat also havepositive temperature coefficients. However, Svptat does not have to havea large temperature coefficient, unlike Tvptat2 shown in FIG. 11.

[0232] The second voltage generating circuit operates in the same manneras that shown in FIG. 18. When Vptat′ is applied to the gate of n-typetransistor M6 from the junction point between the source of transistorM3 and resistor R2, a voltage Vref resulting from addition of Vpn andVptat′ is generated between the source and the gate of the n-typetransistor M7. Since Vref is the sum of Vpn having a negativetemperature coefficient and Vptat′ having a positive temperaturecoefficient, the resultant Vref (the first reference voltage) does nothave a temperature coefficient. Based on the first reference voltageVref, the second reference voltage Tvref and two types of thirdreference voltages Sverf1 and Svref2 are generated through the voltageconversion using resistors R4, R5 a, R5 b, and R6. The referencevoltages Vref, Tvref, Svref1, and Svref are expressed by equations (8),(9), (10)′ and (10)″.

Vref=Vptat*(R 2+R 3)/R 3+Vpn=Vptat′+Vpn   (8)

Tvref=Vref*(R 5 a+R 5 b+R 6)/(R 4+R 5+R 6)   (9)

Svref1=Vref*R 6/(R 4+R 5 a+R 5 b+R 6)   (10)′

Svref2=Vref*(R 5 b+R 6)/(R 4+R 5 a+R 5 b+R 6)   (10)″

[0233] The temperature characteristics of these signals are illustratedin FIG. 27B.

[0234] The operation of the first subtraction circuit is the same as thesubtraction circuit shown in FIG. 18, except for that Svref1 is used inplace of Sverf. Accordingly, the output Tvptat1 of the operationalamplifier OP2 becomes

Tvptat1=(R 8/R 7)*(Svptat−Svref1′).   (11)′

[0235]FIG. 27C illustrates the temperature characteristics of thesesignals processed in the first subtraction circuit. The dotted line A1indicates the subtraction result of (Svptat−Svref1′).

[0236] When the temperature is lower than T1, Svptat<Svref1 stands, andtherefore, Tvptat1 becomes 0 volts. If the temperature is higher thanT1, Svptat>Svref1 stands, and equation (11)′ applies. From equations(11)′ and (16), the ratio S1 of the temperature coefficient (or theslope) of Tvptat1 to that of Vptat is expressed as

S1=[(R 1+R 2+R 3)/R 3]*R 8/R 7.   (17)′

[0237] By simply adjusting the resistances R1, R2, R3, R7 and R8, theratio S1 defined by equation (17)′ can be easily made equal to the ratio(R1+R2+R5)/R5, which is the temperature coefficient of Tvptat obtainedin the first embodiment. For instance, if the temperature coefficient ofTvptat generated in the first voltage generating circuit shown in FIG. 4is fifty (50), the temperature coefficient ratio (R1+R2+R3)/R3] definedin the first voltage generating circuit of the fifth embodiment is setto 10, and the temperature coefficient ratio R8/R7 defined in the firstsubtraction circuit is set to 5. By so setting, the ratio S1 (that is,the temperature coefficient ratio of Tvptat1) becomes fifty (50), as inthe circuit disclosed in the first embodiment, without causing the firstvoltage generating circuit itself to produce Tvptat having a largetemperature coefficient.

[0238] The same applies to the second subtraction circuit. The outputTout2 of the operational amplifier OP12 is expressed as

Tvptat2=(R 18/R 17)*(Svptat−Svref2′)   (11)″

[0239]FIG. 27D illustrates the temperature characteristics of thesesignals processed in the second subtraction circuit, in which the dottedline A2 indicates the subtraction result of (Svptat−Svref2′).

[0240] When the temperature is lower than T2, Svptat<Svref2 stands, andtherefore, Tvptat2 becomes 0 volts. If the temperature is higher thanT1, Svptat>Svref2 stands, and equation (11)″ applies. From equations(11)″ and (16), the ratio S2 of the temperature coefficient (or theslope) of Tvptat2 to that of Vptat is expressed as

S2=[(R 1+R 2+R 3)/R 3]*R 18/R 17.   (17)″

[0241] By simply adjusting the resistances R1, R2, R3, R17 and R18, theratio S2 defined by equation (17)″ can be easily made equal to the ratio(R1+R2+R5)/R5, which is the temperature coefficient of Tvptat obtainedin the first embodiment.

[0242] For instance, if the temperature coefficient of Tvptat generatedin the first voltage generating circuit shown in FIG. 4 is fifty (50),the temperature coefficient ratio (R1+R2+R3)/R3] defined in the firstvoltage generating circuit of the fifth embodiment is set to 10, and thetemperature coefficient ratio R18/R17 defined in the second subtractioncircuit is set to 5. By so setting, the ratio S2 (that is, thetemperature coefficient ratio of Tvptat2) becomes fifty (50), as in thecircuit disclosed in the first embodiment, without causing the firstvoltage generating circuit itself to produce Tvptat having a largetemperature coefficient.

[0243] In the first comparison circuit, if the temperature is lower thanT1, Tvref>Tvptat1 stands, and output Tout1 of the comparator(operational amplifier OP3) becomes High. If the temperature is higherthan T1, Tvref<Tvptat2 stands, and therefore, the output Tout1 becomesLow.

[0244]FIG. 27E illustrates the temperature characteristics of thesignals processed in the first and second comparison circuits. In thesecond comparison circuit, if the temperature is lower than T2.Tvref>Tvptat2 stands, and output Tout2 of the comparator (operationalamplifier OP13) becomes High. If the temperature is higher than T2,Tvref<Tvptat2 stands, and therefore the Tout2 becomes Low. These outputsignals Tout1 and Tout2 are used as control signals for a semiconductorintegrated circuit, which can control the operation of the semiconductorintegrated circuit at two different temperatures.

[0245]FIG. 29 illustrates the temperatures characteristics of Tptat1 andTptat2 generated in the fifth embodiment, as compared with Tptatgenerated in the first embodiment. In the fifth embodiment, Svptatgenerated by the first voltage generating circuit is not so large, andthis Svptat is further reduced to lower levels in two differenttemperatures ranges by subtracting Svref1 and Svref2 by the first andsecond subtraction circuits, respectively. The subtraction results areamplified to produce Tvpat1 and Tvpat2. These voltages Tvptat1 andTvptat2 shift to lower levels with the same temperature coefficients asTvptat, and consequently, the operation voltage of the entiretemperature sensor can be reduced.

[0246] As in the fourth embodiment, Svref1 and Svref2 may be inputalternately to a single subtraction circuit by switching the pathbetween Svref1 and Svref2.

[0247] In this manner, the temperature sensor of the present inventioncan operate in at least one of the highly-sensitive operating mode andthe low-voltage operating mode.

[0248] With the configuration of the first embodiment, the temperaturesensor operates in either the highly-sensitive operating mode or thelow-voltage operating mode. With the configurations of the secondthrough fifth embodiments, the temperature sensor can operate at highsensitivity, and at the same time, at a low operating voltage.

[0249] With the configurations of the fourth and firth embodiments, thetemperature sensor can sense two different operating temperaturesprecisely at low operating voltage.

[0250] This patent application is based on and claims the benefit of theearlier filing dates of Japanese patent application No. 2002-081448filed Mar. 22, 2002 and Japanese patent application No. 2003-028514filed Feb. 5, 2003, the entire contents of which are hereby incorporatedby reference.

What is claimed is:
 1. A temperature sensor comprising: a first voltagegenerating circuit that generates and outputs a first voltage having apositive or negative temperature coefficient in proportion to theabsolute temperature; a second voltage generating circuit that generatesa second voltage having an opposite sign of temperature coefficientcompared to the first voltage, and outputs a reference voltage that doesnot have a temperature coefficient based on the second voltage; and acomparator that compares the first voltage output from the first voltagegenerating circuit with the reference voltage output from the secondvoltage generating circuit.
 2. The temperature sensor according to claim1, wherein the first voltage generating circuit generates and outputs athird voltage having the same sign of temperature coefficient as thefirst voltage and having the same absolute value as the second voltage,and the second voltage generating circuit produces the reference voltageby adding the second voltage to the third voltage supplied from thefirst voltage generating circuit.
 3. The temperature sensor according toclaim 1, wherein the second voltage generating circuit generates a thirdvoltage having the same sign of temperature coefficient as the firstvoltage and having the same absolute value as the second voltage, andproduces the reference voltage by adding the second voltage to the thirdvoltage.
 4. The temperature sensor according to claim 1, wherein thefirst voltage generating circuit includes two or more transistors of asame conductivity type and with different impurity concentrations ofgates.
 5. The temperature sensor according to claim 1, wherein the firstvoltage generating circuit includes a first transistor having ahighly-doped n-type gate, a second transistor having a lightly-dopedn-type gate, and a source follower that gives a gate potential to thesecond transistor.
 6. The temperature sensor according to claim 5,wherein the source follower is comprised of a third transistor and twoor more resistors whose resistance values are adjustable, and the firstvoltage is output from the source follower to the comparison circuit. 7.The temperature sensor according to claim 1, wherein the second voltagegenerating circuit includes two or more transistors having differentgate polarities.
 8. The temperature sensor according to claim 1, whereinthe second voltage generating circuit includes a first transistor havinga highly-doped n-type gate, a second transistor having a highly-dopedp-type gate, and a source follower giving a gate potential to the secondtransistor.
 9. The temperature sensor according to claim 8, wherein thesource follower is comprised of a third transistor and two or moreresistors whose resistance values are adjustable, and the referencevoltage is output from the source follower to the comparison circuit.10. The temperature sensor according to claim 1, wherein the comparisoncircuit includes a first transistor and a second transistor thatfunction as input transistors of a differential amplifier, and the firstvoltage is applied to the gate of the first transistor, while thereference signal is applied to the gate of the second transistor.
 11. Atemperature sensor comprising: a first voltage generating circuit thatgenerates a first voltage having a positive or negative temperaturecoefficient; a second voltage generating circuit that generates a firstreference voltage and a second reference voltage that do not have atemperature coefficient; a subtraction circuit that subtracts the firstreference voltage supplied from the second voltage generating circuitfrom the first voltage supplied from the first voltage generatingcircuit, and outputs a subtraction result; and a comparison circuit thatcompares the subtraction result output from the subtraction circuit withthe second reference voltage supplied from the second voltage generatingcircuit, and outputs a comparison result.
 12. The temperature sensoraccording to claim 11, wherein the second voltage generating circuitgenerates a second voltage having a positive or negative temperaturecoefficient, and a third voltage having an opposite sign of temperaturecoefficient compared to the second voltage, and wherein the first andsecond reference voltages are generated based on the sum of the secondand third voltage.
 13. The temperature sensor according to claim 11,wherein the first voltage generating circuit generates and outputs asecond voltage having the same sign of temperature coefficient as thefirst voltage to the second voltage generating circuit, and the secondvoltage generating circuit generates a third voltage having an oppositesign of temperature coefficient compared to the first voltage and havingthe same absolute value as the second voltage, and adds the thirdvoltage to the second voltage to produce the first and second referencevoltages.
 14. The temperature sensor according to any one of claims 11through 13, further comprising another set of subtraction circuit andcomparison circuit, wherein the second voltage generating circuitoutputs two values of the first reference voltage for the twosubtraction circuits, and the temperatures sensor outputs two comparisonresults at different temperatures.
 15. The temperature sensor accordingto claim 11, wherein the first voltage generating circuit includes twoor more transistors that are of a same conductivity type and withdifferent impurity concentrations of gates.
 16. The temperature sensoraccording to claim 11, wherein the first voltage generating circuitincludes a first transistor having a highly-doped n-type gate, a secondtransistor having a lightly-doped n-type gate, and a source followercomprised of a third transistor and at least one resistor, and whereinthe source follower gives a gate potential to the second transistor. 17.The temperature sensor according to claim 11, wherein the second voltagegenerating circuit includes two or more transistors having differentgate polarities.
 18. The temperature sensor according to claim 11,wherein the second voltage generating circuit includes a firsttransistor having a highly-doped n-type gate, a second transistor havinga highly-doped p-type gate, and a source follower comprised of a thirdtransistor and at least one resistor, and wherein the source followergives a gate potential to the second transistor.
 19. The temperaturesensor according to claim 11, wherein the subtraction circuit includes:a differential amplifier comprised of a first operational amplifier andfirst through fourth resistors; and a voltage follower comprised of asecond operational amplifier.
 20. The temperature sensor according toclaim 18, wherein the subtraction circuit includes a differentialamplifier that is comprised of a first operational amplifier and firstthrough fourth resistors, and wherein the resistance values of the firstthrough fourth resistors are set greater than that of said at least oneresistor of the source follower of the second voltage generatingcircuit.
 21. The temperature sensor according to claim 20, wherein thefirst reference voltage is output from the source follower of the secondvoltage generating circuit to the first operational amplifier of thesubtraction circuit.
 22. The temperature sensor according to claim 18,wherein the subtraction circuit includes: a differential amplifiercomprised of a first operational amplifier and first through fourthresistors; and a voltage follower comprised of a second operationalamplifier, and wherein the first reference voltage is output from thesource follower of the second voltage generating circuit to the firstoperational amplifier of the subtraction circuit.